Winner! Had lots of racing customers with these broken and no source, I know folks with a half dozen broken transmissions because they can't get the part. So, we finally ran a batch of the upgraded part that Mazda MotorSports was carrying years ago.
This 3rd 4th gear shift weakness is a know issue for a long time. But only few people pay attention about it, or even knew it. I have explored it back in 07 but decide to leave it alone since my NC see relatively low track time (compare to race team) and my driving style is relatively gentle in shifting and clutching. However, for sure I will do a swap if I open the tranny box.